Effect of Cr Substitution on the Formation and Fuctuation-Induced Conductivity Analysis of (Tl_1-xCr_x)Sr₂CaCu₂O₇ Superconductor

Abstract

The (Tl1-xCrx)Sr2CaCu2O7 (Tl-1212) sample with nominal starting composition for x = 0.0, 0.2 and 0.3 were prepared by the solid-state reaction method. The samples were studied by powder x-ray diffraction method and electrical resistance versus temperature measurement. Excess conductivity analysis was carried out using the Aslamazov–Larkin (AL) theory, and the dimension of fluctuation-induced conductivity (λ) was determined. The Lawrence–Donaich (LD) theory was used to calculate the coherence length (ξc(0)), Josephson coupling (J), and γ = (ξab(0)/ξc(0)) of the superconductive samples. Excess conductivity analysis showed that Cr substitution induced 2D-to-3D conductivity transition at the highest transition temperature (T2D-3D) observed at x = 0.3. The calculations based on the Lawrence–Doniach model revealed that the shortest coherence length and weakest inter-plane coupling (J) occurred when x = 0.2. The sample with x = 0.2 and 0.3 showed the Tl-1212 as the major phase. The highest onset temperature of 110 K was observed in the x = 0.2 sample. Our result showed that the formal value of 2.3+ is more important than the Josephson interlayer coupling J in optimizing the transition temperature.